When belt drives were replaced by air-driven turbines for rotating dental burs, the very high speed of the turbines permitted drilling and other dental operations to be done much faster and with less trauma to the patient than in prior times. The high speed of the rotating parts however, caused several problems not associated with the belt-drive technology. Foremost among the problems were excessive noise, adequate bearing support, and a need for a controlled axial load to prolong bearing life.
Early in the development of turbine driven handpieces a removable cartridge consisting of rotating parts and bearings, and sometimes an enclosing cylinder, was used in the head of the handpiece. An example of a cartridge having a tangential flow turbine is shown in U.S. Pat. No. 3,074,167, while a cartridge with an axial flow turbine in it is shown in U.S. Pat. No. 3,411,210. In these patents, the cartridges were mounted directly in the handpiece housings without any accoustical isolation. The handpieces were quite noisy, and very precise machining of the housing bores was required to prevent outer race rotation of the ball bearings, yet not hold the outer races too tightly.
Noise reduction by isolating the cartridge from the housing through elastomeric rings has been achieved in several ways. In U.S. Pat. No. 3,218,028 one version of the cartridge uses two resilient bushings, while a second version uses two O-rings. Four O-rings are used in U.S. Pat. No. 3,268,205. While O-rings reduce noise and provide bearing support, they do not provide sealing or axial bearing pre-loading.
Formed noise-reducing collar members are shown in U.S. Pat. No. 3,134,172, while vibration absorbers having similar cylindrical and flanged elements are shown in U.S. Pat. No. 3,376,084. While the flanged sections of these rings form an axial loading means, the solid, thin flanges have a very high spring rate, making reliable control of the axial force very difficult to achieve.